Polyimide film has been widely used in various technical fields because it exhibits excellent high-temperature resistance, excellent chemical-resistance properties, high insulation, and high mechanical strength. For example, polyimide film is advantageously used in the form of a composite sheet of successive aromatic polyimide film/metal film to produce a flexible printed circuit (FPC), a carrier tape of tape automated bonding (TAB), and a lead-on-chip (LOC) structural tape. Especially, the flexible printed circuit board has been broadly applied to materials of laptops, consumer electronic products, and mobile communication equipments.
In the production of printed circuit board, it mainly uses high temperature resistance adhesive agent to apply on a polyimide insulation film, and then laminate with a metal foil such as copper foil, to produce flexible printed circuit board, which is in turn applied to materials of laptops, consumer electronic products, and mobile communication equipments.
The adhesive agent currently used is thermoplastic polyimide system, which has a high heat expansion coefficient, poor heat resistance and poor dimension stability. Moreover, the lamination between the polyimide insulation film and the metal foil should be carried out at an elevated temperature.
In view of the above drawbacks resulted from the use of thermoplastic adhesive agent in production of flexible printed board, there needs an adhesive agent for laminating polyimide film and a metal foil while capable of overcoming the high heat expansion coefficient of thermoplastic polyimide and improving heat resistance and dimension stability without carrying out at an elevated temperature.
The present inventors have conducted an investigation on the structure of polyimide resin and developed a polyimide resin composition modified with bismaleimide and cyanate, which is capable of overcoming the above problems, and thus completed the present invention.